1. Field of the Invention
The present invention pertains generally to bipolar transistor structures, and more particularly to bipolar transistor structures incorporated into integrated circuits.
2. Description of the Background Art
In the current state of the art, mainstream silicon bipolar transistor structures are typically processed using self-aligned, double polysilicon, trench-isolated technology. Although improved over the years, with many new materials and processes introduced, those transistor structures are still based on similar geometry as the first double-diffused, pn-junction isolated, silicon bipolar devices; that is, the placement of electrodes, vertical current flow and interconnection system are basically the same. Heterojunction bipolar transistors are based on the same geometry, as well, although the technology is much different than that of Si/SiGe based devices.
Another family of bipolar structures, those with horizontal current flow, are primarily fabricated in silicon technology and are called lateral bipolar transistors (LBTs). LBTs are mainly processed using silicon-on-insulator (SOI) technology. Those transistors often exhibit inferior high-frequency characteristics compared to state-of-art silicon substrate devices. There are LBT's processed in Si-substrate technology, but they are either lateral pnp transistors or CMOS-process-incorporated npn transistors. Lateral pnp transistors are non-optimized devices processed in npn-based technology with inferior electrical characteristics compared to mainstream npn transistors. CMOS compatible npn LBT's are also non-optimized devices, processed in CMOS-based technology with poor electrical characteristics.
Therefore, there is a need for a bipolar transistor structure that overcomes some of traditional bipolar transistor disadvantages (e.g. complicated technology, large transistor area, inability to scale down), and which can extend the market of bipolar technology. The present invention satisfies those needs, as well as others, and overcomes deficiencies in current bipolar transistor technology.